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External morphology of the erect glans penis of the dog.

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External Morphology of the Erect Glans
Penis of the Dog '
BENJAMIN L. HART2 AND RALPH L. KITCHELL3
Department of Veterinary A n a t o m y ,
University of Minnesota, S t . Paul, Minnesota
ABSTRACT
The external morphology of the erect glans penis was studied and
compared to that of the nonerect organ. Morphological changes that occur with
tumescence and detumescence were also reported. Some distinct parts of the erect
pars longa glandis which are not distinguished i n classical nomenclature are described
and labeled. These structures are the urethral process, corona glandis and collum
glandis. These distinct morphological areas coincide with areas which seem to be
functionally distinct in both the erect and nonerect glans penis. The implications
that these observations may have for considerations of comparative anatomy of the
external male genitalia are discussed
The external morphology of the glans
penis of mammals varies greatly from
species to species. In these mammals the
anatomical description of structures such
as the urethral process, corona glandis and
collum glandis is based on the appearance
of the nonerect or flaccid penis. We became interested in comparing the morphology of the nonerect penis to the erect
penis as a result of previous studies on
spinal sexual reflexes elicited by genital
stimulation (Hart, '64). Initially it was
assumed that stimulation of any area of
the glans would have about the same effect
as any other on the reflexes observed. It
soon became apparent, however, that
stimulation of one area of the glans
had effects entirely different from stimulation of another area (even in the nonerect penis). After repeated observation
of these effects, it was also noted that,
in the erect glans penis, different structures
were visibly discernible which were not
apparent in the nonerect state and had not
been described previously (Ellenberger and
Baum, '43; Miller, '52; Miller, Christensen
and Evans, '64; Sisson and Grossman, '53;
Bradley, '59; Nickel, Shummer and Seiferle,
'60). These areas, which were grossly visible as distinct structures, were the same
areas which, when stimulated, resulted in
different functional responses. It is the
purpose of this paper to first compare the
erect penis of the dog to the nonerect organ
in regard to external morphology and,
secondly, to discuss the implications of
ANAT. REC.,152: 193-198.
these findings for classical anatomical
nomenclature.
MATERIALS AND METHODS
The experimental subjects were adult
mongrel male dogs. The progression of
erection was studied visually and recorded
cinematographically.
Two types of experimental procedures
were used. In one group of 15 animals,
erection was elicited by use of an artificial
vagina similar to the one described by
Harrop ('54). When a full erection had
been obtained, the vagina was removed.
In the second group of animals, totaling
16 ( 4 were previously members of the
first group), a spinal transection was performed, and the animals were maintained
in the chronic spinal state from 40 to 185
days. The procedure for the spinal transection and postoperative care is presented
elsewhere (Hart, '64). In the chronic
spinal preparation, an erection was easier
to elicit without the use of an artificial
vagina, by merely holding the penis behind
the bulbus glandis and rubbing the area
surrounding the external urethral orifice.
The progression and subsidence of erection
1 This investigation was supported in part by Public Health Service Training Grant 5T1-GM-386-04 from
the Division of General Medical Sciences. Based i n
part on a thesis submitted by the senior author to the
Graduate School of the University of Minnesota, i n
partial fulfillment of the requirements for the Ph.D.
degree.
2 Present address: Department of ,Anatomy, University of California, Davis, Califomla.
3 Present address: College of Veterinary Medicine,
Kansas State University, Manhattan, Kansas.
193
194
BENJAMIN L. HART AND RALPH L. KITCHELL
was observed and recorded cinematographically in this second group.
Brief review of anatomy
of the canine penis
In order to facilitate discussion of the
results, the anatomy of the penis will be
briefly reviewed. The canine penis consists of a root, body and glans. The root
is a paired structure composed of two crura
which arise from the ischial tuberosities of
the pelvic girdle. The body is the portion
of the penis extending from the union of
the two crura to the glans. The glans or
distal portion is quite long in the dog and
is divided into a caudal or proximal bulbous part, the bulbus glandis and a cranial
or distal part, the pars longa glandis. Since
the prepuce is reflected onto the glans
about halfway between the two extremities
of the bulbus, the glans is the only portion
of the penis that can ordinarily be exposed
by pushing back the sheath. The rest of
the penis can be easily palpated, however.
In the center of the penis is a bone (0s
penis) extending from the distal portion of
the body to almost the tip of the glans.
When the penis is not erect this bone helps
keep the organ relatively rigid.
The most extensive erectile tissue of the
penis is the corpus cavernosum urethrae
(spongiosum). This structure surrounds
the urethra within the pelvic cavity and
extends in this relationship throughout the
entire length of the penis. Just proximal
to the entrance of the pelvic portion of the
corpus ca,vernosum urethrae into the body
of the penis, this cavernous body gives off
two bulbous expansions which project
proximally between the two crura of the
root. These are the so-called bulbs of the
urethra. The bulbus glandis is a cavernous
dorsal expansion of the corpus cavernosum
urethrae. The erectile tissue of the crura
of the root is the paired corpus cavernosum
penis. This is the least expansive of the
erectile bodies of the penis. The erectile
tissue of the pars longa glandis is separated from the erectile tissue of the bulbus
glandis by a fibrous sheath, but it is similar in structure and expansive characteristics.
The extrinsic muscles of the penis are
the striated bulbocavernosus, ischiocavernosus and ischiourethral muscles. The
canine penis also contains a retractor penis
muscle. The retractor is composed mostly
of smooth muscle fibers and extends from
the first and second coccygeal vertebrae to
insert on the penis near the fornix of the
prepuce. The bulbocavernosus muscle
arises from the external anal sphincter.
The ischiocavernosus muscle originates
from the ischial tuberosity and inserts on
the corpus cavernosum penis. The ischiourethral muscle is paired and also originates on the ischial tuberosity adjacent to
and cranio-dorsal to the origin of the ischiocavernosus muscle. The insertion of the
ischiourethral muscle is onto a fibrous ring
encircling the common trunk of the left
and right dorsal veins of the penis.
The glans penis of the dog, according to
classical gross description and terminology,
is divisible only into a pars longa glandis
and bulbus glandis. No other structures,
such as a n urethral process, corona or collum, some of which are described for other
species such a s man, the stallion, the bull
and the ram, have been labeled. The reason for this undoubtedly is because the
penis in the erect state has not been carefully studied.
RESULTS
The penis of one of the dogs as erection
progressed from the nonerect state to complete erection is shown in figure 1. It was
clear that as erection progressed certain
structures of the pars longa glandis became
quite prominent.
Though the nonerect glans has essentially the same appearance in all of the
dogs observed, there is considerable variation in external morphology among the
animals. The ranges of differences in the
erect state observed is shown in the four
specimens presented in figure 2.
During functional studies (Hart, '64)
stimulation of these morphologically distinct regions of the erect penis evoked distinctly different responses in both the intact and the spinal preparation. Since these
studies necessitated repeated reference
to the respective parts, some new terms
have been introduced to describe these regions. The terminology used is in keeping
with what would probably be analogous
parts in other domestic species (fig. 3). At
the free extremity of the erect pars longa
Fig. 1 Photographs to illustrate morphological changes during the progression of erection
i n the glsns penis. The prepuce is held behind the bulbus glandis in all pictures. ( A ) Nonerect (holding the sheath back has forced a protrusion of the epithelium over the 0 s penis
at the free end of the pars longa glandis); ( B ) and ( C ) stages intermediate between the
nonerect and the completely erect glans; ( D ) complete erection.
195
Fig. 2 Photographs to illustrate variations in morphology in the erect glans penis of the
dogs studied. All of the animals were mongrels so no specific references could be made
to breed.
196
MORPHOLOGY O F THE GLANS PENIS
glandis an “urethral process” is quite apparent. At the apex of the process is the
external urethral orifice. Just caudal to
the urethral process is a distinct corona,
and hence this will be termed the “corona
glandis.” Both the urethral process and
the corona are, in the erect glans, deep
scarlet in color and have a wrinkled surface (figs. 1 and 2). The portion of the
pars longa glandis extending from the
corona to the bulbus glandis will be called
the “collum glandis.” The collum is turgid
and usually has a bluish-white appearance.
The appearance of these parts of the
pars longa glandis during erection and subsidence of erection was also studied. The
mechanism of erection with regard to en-
gorgement of the cavernous spaces is reviewed and described by Christensen (’54).
However, since the terminology introduced
above was not used by Christensen, changes
in these structures were not described by
him.
The erectile process was divided into
four stages to facilitate description of erection. The first change at the commencement of erection is an engorgement of cavernous spaces in the crura of the penis.
This engorgement does not increase the
diameter of the penis to any noticeable extent; it serves mostly to stiffen the organ.
The next region to become engorged is the
bulbus glandis. When the bulbus has become markedly engorged, “stage one” has
Nonerect
S t a a e one
S t a g e two
S t a a e three
Stage four
Subsiding
Corona
glandis
Collum
glandis
Fornix
\
Urethral
process
L
Pars longo
glandis
197
Bul bus
glandis
Fig. 3 Drawings made by projecting frames taken from a motion picture of the progression and subsidence of erection. The prepuce has been reflected proximally to expose
the bulbus glandis. “Stage four” is used as the reference in labeling the various parts of
the glans penis. Erection was elicited by holding the penis caudal to the bulbus glandis
and rubbing the urethral process.
198
BENJAMIN L. HART AND RALPH L. KITCHELL
been attained. In some cases, the bulbus
glandis may increase in size to the extent
that it reaches almost maximum distention
before the pars longa glandis starts to enlarge. When the pars longa glandis has
increased noticeably in diameter and the
urethral process has become extended,
“stage two” has been reached. Since “stage
four” is defined as complete erection, “stage
three” is taken as the interval between the
second and fourth stages. During the interval of “stage three,” the glans continues
to increase in diameter, and the corona
glandis becomes prominent. In “stage
four” the urethral process and corona are
at their maximum distention although the
process does not appear to be as prominent
as in the preceding stage. This is because,
during the “third stage,” the corona has
become disproportionately more engorged
than the process, and the corona has encroached upon the caudal aspect of the
process. With complete erection, the contrast between the scarlet red urethral process and corona and the bluish-white collum
and bulbus is most apparent (figs. 2 and 3).
Subsidence of erection is not the converse of tumescence. The engorged bulbus
subsides markedly before detumescence begins in the pars longa glandis. As erection
continues to subside, the corona and
urethral process become especially prominent because the detumescence of the pars
longa glandis takes place first in the collum glandis (fig. 3 ) .
DISCUSSION
The terms used to label the parts of the
penis are those which are used to label
what are probably comparable structures
in other species. The glans penis of the
horse, for example, possesses an urethral
process, a corona and a collum in somewhat the same topographical arrangement.
However, a troublesome point in this analogy is the existence of a prominent bulbus
glandis in the canine species more proximal than the collum glandis. None of the
other common domestic species have a
bulbus glandis. In man the collum glandis
or neck appears to be the most proximal
part of the glans (Markee, ’53; Grant, ’62).
Since the horse does have a processus dorsalis glandis located more proximally on
the penis than the collum, it does seem
appropriate to use the terminology suggested.
The results of this work raise a question
of general anatomical description and
labeling. When a structure becomes extremely modified in one physiological state
to the extent that distinct structures become evident which are hardly discernible
in another state, upon which of the two
states should naming and classification of
structures be based? The reason, obviously,
that the urethral process and corona have
not been described for the dog is that little
work has been done on the erect organ
from a functional and morphological
standpoint. The point is once again to be
emphasized that the study of anatomy on
the cadaver is often misleading and that,
when functional aspects are considered,
the classical species differences may be
more superficial than erstwhile believed.
LITERATURE CITED
Bradley, 0. C. 1959 Topographical Anatomy of
the Dog, 6th Ed. Oliver and Boyd, Edinburgh.
Christensen, G. C. 1954 Angioarchitecture of
the canine penis and the process of erection.
Am. J. Anat., 95: 227-261.
Ellenberger, W., and H. Baum 1943 Handbuch
der Vergleichenden Anatomie der Haustiere.
Revised by 0. Zeitzschmann, E. Ackerknect
and H. Grau. Springer, Berlin.
Grant, J. C. B. 1962 An Atlas of Anatomy, 5th
Ed. Williams and Wilkins, Batlimore.
Harrop, A. E. 1954 A new type of canine artificial vagina. Brit. Vet. J., 110: 194-195.
Hart, B. L. 1964 Spinal sexual reflexes in the
male dog and their relation to sexual behavior.
Ph.D. Thesis, University of Minnesota.
Markee, J. E. 1953 The Urogenital System. In:
Morris’ Human Anatomy, 11th Ed., J. P.
Schaeffer, Ed. pp. 1493-1569. McGraw-Hill,
New York.
Miller, M. E. 1952 Guide to the Dissection of
the Dog, 3rd Ed. Published by the author,
Ithaca, New York.
Miller, M. E., G. C. Christensen and H. E. Evans
1964 Anatomy of the Dog. W. B. Saunders,
Philadelphia.
Nickel, R., A. Schummer and E. Seiferle 1965
Lehrbuch der Anatomie der Haustiere. Paul
Parey, Berlin and Hamburg.
Sisson, S., and J. D. Grossman 1953 The Anatomy of the Domestic Animals, 4th Ed. W. B.
Saunders, Philadelphia.
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